Double wall corrugated lng tank

ABSTRACT

A double wall tank for the marine transportation of liquefied natural gases at atmospheric pressure and cryogenic temperature, the tank having its primary and secondary barriers supported in such a way that the respective barrier supports are in alignment. The walls of the inventive tank, in its preferred embodiment, are corrugated in a horizontal direction. All liquid-tight welds are either butt or seam welds, and all transitions between the walls of the tank are smooth, without intermediate box girders. A plurality of vertical webs support the primary barrier of the tank; and a plurality of diaphragms, intermediate the primary and secondary barriers, are positioned in alignment with the vertical webs and support the secondary barrier. The vertical webs are stabilized by lightweight channel-shaped struts; corner plates support the corners of the tank and serve as base members for the struts. The tank is supported and keyed at the bottom only, thereby reducing the load transmitted to the structure of the ship near the top of the tank.

Limited States Patent [191 Bridges et a1.

TANK

Filed:

Inventors: Thomas DOUBLE WALL CORRUGATED LNG F. Bridges; George R.

-Knight, Jrz, both of Port Washington, N.Y.; Ivan Mertll, Greenwich,Conn.

Assignee: John J. McMullen Associates, Inc,

New York, NY.

Sept. 9, 1970 Appl. No.: 70,869

[52] US. Cl. ..220/9 LG, 114/74 A, 220/10, 220/15, 220/71 [51] Int. Cl...lB65d 25/18 [58] Field of Search .....220/15, 9 LG, 71, 72, 83,10,220/1 B, 22, 16; 62/45; 114/74 A [56] References Cited UNITED STATESPATENTS 900,166 10/1908 Harry ..220/10 1,807,912 6/1931 Hansson ..220/721,886,197 ll/1932 Kramer..... ...220/DIG. 24 2,927,711 3/1960Naggiar.... ..220/15 X 2,963,873 12/1960 Stowers .114/74 A X 3,313,1164/1967 Nonnecke et al. ..62/45 3,314,567 4/1967 Becker et a1. ..220/153,319,431 5/1967 Clarke et a1. 220/9 LG X 3,425,583 2/1969 Bridges..220/15 3,428,205 2/1969 Basile et a1. .....220/l5 3,570,702 3/1971Yamamoto ..220/22 X ]March 20, 1973 FOREIGN PATENTS OR APPLICATIONS555,624 9/1957 Belgium ..220/22 1,054,641 1/1967 GreatBr-itain ..l14/74A[5 7 ABSTRACT A double wall tank for the marine transportation ofliquefied natural gases at atmospheric pressure and cryogenictemperature, the tank having its primary and secondary barrierssupported in such a way that the respective barrier supports are inalignment. The walls of the inventive tank, in its preferred embodiment,are corrugated in a horizontal direction. All liquid-tight welds areeither butt or seam welds, and all transitions between the walls of thetank are smooth, without intermediate box girders. A plurality ofvertical webs support the primary barrier of the tank; and a pluralityof diaphragms, intermediate the primary and secondary barriers, arepositioned in alignment with the vertical webs and support the secondarybarrier. The vertical webs are stabilized by lightweight channel-shapedstruts; corner plates support the corners of the tank and serve as basemembers for the struts. The tank is supported and keyed at the bottomonly, thereby reducing the load transmitted to the structure of the shipnear the top of the tank.

23 Claims, 11 Drawing Figures PATEIETFPHARZOISYS SHEET 20? 6 111 1111171nllllllrlr DOUBLE WALL CORRUGATED LNG TANK BACKGROUND OF THE INVENTIONIn copending U.S. patent application Ser. No. 732,009, now U.S. Pat. No.3,670,517, a streamlined continuation of its parent application filed onMar. 16, 1965, assigned to the present assignee, a double wallcorrugated tank for the marine transportation of liquefied natural gasesis disclosed. In this patent application the corrugations in the sidewalls of the tank are l vertically oriented while the corrugations inthe top and bottom walls of the tank are horizontally oriented. Four boxgirders are provided at the top of the tank and four similar box girdersare provided at the bottom of the tank. The top, bottom and side wallsof the tank, with their corrugations, are T-welded to the respective boxgirders. The walls of the tank are supported and stabilized by internalvertical webs, between-wall diaphragms and horizontal stringers.

Because of its design, the tank disclosed in the above-noted copendingpatent application has numerous drawbacks. First, since a large numberof T- welds appear both in the primary and secondary barriers,liquid-tight construction becomes a difficult task. The T-weld is noteasily made liquid-tight; and a radiographic leak detection procedure iscorrespondingly difficult. In addition, the T-welds result in localpoints of stress concentration. And, further, the need for box girdersystems adds both to the weight and the cost of the cargo tank.

In this copending patent application, the secondary barrier of thedisclosed tank is supported by a plurality of diaphragm plates; and theprimary barrier is supported by a number of vertical webs. To stabilizethe vertical webs, a plurality of horizontal stringers is provided. Thisconstruction, while effective, tends to be overly complex and, becauseof its complexity, tends to be somewhat heavy.

In many of the tanks known to the prior art, the supporting function andthe keying function are performed by distinct structures. Further, thetanks are often supported at a number of positions around its periphery.Su'ch arrangements, it has been found, tend to be somewhat uneconomicaland overly complex. In addition, it has been found that the tank loadshave often been transmitted to the structure of the ship near the top ofthe tank, thereby causing stress in the ship structure.

It is toward the elimination of the above-noted drawthat the presentinvention is directed.

SUMMARY OF THE INVENTION The present invention relates to a double walltank for the marine transportation of liquefied natural gases atatmospheric pressure and cryogenic temperature. The inventive tank iscorrugated throughout, and has many economic advantages over those tanksknown to the prior art.

With the corrugated tank of the present invention, smooth transitionsbetween tank walls are provided. In this manner, all T-welds and each ofthe problems associated therewith are avoided. The elements of theinventive tank, both in the primary and secondary barriers, are eitherbutt welded or are seam welded. Therefore, the welds may more easily bemade liquid-tight.

And, because of the smooth transitions without T- welds, theconventional points of high stress concentration have been eliminated.Further, butt and seam welds may readily be checked for liquid-tightoperation by the use of radiographic techniques; as noted above,radiographic analysis is quite difficult with T-welds. In the preferredembodiment of the inventive tank, all of the walls have theircorrugations aligned in the horizon- 0 tal direction.

In the horizontally corrugated embodiment of the double wall tankforming a part of the present invention, the primary barrier issupported by a plurality of vertical webs located within the primarybarrier. Diaphragms are positioned intermediate the primary andsecondary barriers, and in alignment with the vertical support thesecondary barrier. With the vertical webs and the diaphragms so aligned,the need for horizontal stringers is eliminated. As a result, there is alarge potential weight savings. However, to ensure proper stabilizationof the inner flanges of the vertical webs, relatively lightweightchannel-shaped struts are provided. But even with these struts, there isa substantial savings in weight when comparing the tank of the presentinvention with the tank disclosed in the abovereferenced copendingpatent application.

While the corrugations are preferably aligned horizontally, the presentinvention contemplates that they may be vertically aligned as well.Then, rather than using vertical webs as the primary support members,horizontal stringers would be used. The present invention then involvesaligning the diaphragm plates horizontally with the horizontalstringers.

The inventive tank is supported and keyed in place from the bottom only.This, in comparing the inventive tank with tanks known to the prior art,is quite simple in design and greatly reduces the loads introduced intothe structure of the ship near the top of the tank.

In a first embodiment, the tank of the present invention has enlargedrounded corners providing access between the primary and secondarybarriers. This access facilitates inspection and repair of the twoliquidtight barriers. In a second embodiment, the space between theprimary and secondary barriers is large enough to provide access in adirection perpendicular to the horizontal corrugations. This secondembodiment, while decreasing the carrying capacity of the tank, may befound to be more economical in the end due to the ease of constructiongained by such a configuration and the ease with which inspection may beaccomplished.

Accordingly, it is the main object of the present invention to provide adouble wall tank for the marine transportation of liquefied naturalgases at atmospheric pressure and cryogenic temperature, which tank isconstructed with relative case, which is light in weight, and

members are in alignment, thereby enhancing the effects of thesemembers.

Yet a further object of the invention is to provide a double wallcorrugated cargo tank having smooth between-wall transitions andeliminating the need for T-welds.

Yet another object of the present invention is to provide a double wallcorrugated tank having maximum strength with a minimum number ofstructural elements.

A further object of the present invention is to provide a double wallcorrugated tank requiring no horizontal stringers for purposes ofstrength.

Still a further object of the present invention is to provide acorrugated tank which is supported and keyed on the bottom only.

Another object of the present invention is to provide a double wallcorrugated tank wherein ready access is provided between the walls ofthe tank.

A further object of the present invention is to provide a double wallcorrugated tank wherein access between the walls tank is provided in adirection parallel to the corrugations.

Still another object of the present invention is to provide a doublewall corrugated tank wherein access is provided between the walls of thetank in a direction transverse to the corrugation.

Yet a further object of the present invention is to provide ahorizontally corrugated cargo tank having the qualities recited above.

These and other objects of the present invention, as well as many of theattendant advantages thereof, will become more readily apparent whenreference is made to the following description taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation, partiallyin section, of a ship equipped with a cargo tank constructed inaccordance with the teachings of the present invention;

FIG. 2 is a vertical cross-section of the inventive tank taken alongline 2-2 of FIG. 3;

FIG. 3 is a horizontal cross-section of the inventive tank takenalongline 33 of FIG. 2;

FIG. 4 is a cross-section of the inventive tank taken along line 4-4 ofFIG. 3;

FIG. 5 is a cross-section taken along line 5-5 of FIG. 3;

FIG. 6 is a cross-section of a corrugated wall of the inventive tanktaken along line 6-6 of FIG. 5;

FIG. 7 is a cross-section taken along line 7-7 of FIG. 6;

FIG. 8(a) is a cross-section showing the top and side wall corrugations;

FIG. 8(b) is a cross-section showing the deeper tank bottomcorrugations;

FIG. 9 is a cross-section through line 9-9 of FIG. 2; and

FIG. 10 is a perspective view showing the corner construction of theinventive tank.

DETAILED DESCRIPTION OF THE DRAWINGS With reference first to FIG. 1, aship equipped with a plurality of cargo tanks constructed in accordancewith the teachings of the present invention is shown generally at 10with a portion of the hull 12 cut away to expose a number of cargo tanks14 (only two being shown). As is customary in the field of marinetransportation of cryogenic fluids, it is contemplated that a largenumber of cargo tanks be provided in the holds of the ship 10. The tanks14 are located below the deck 16 of the ship 10 and are entirelysurrounded by a layer of insulation 18, this insulation, for example,taking the form of a number of foam blocks. As shown in FIG. 1, thelayer of insulation 18 is affixed to the outer wall of the tanks 14;however, this insulation may be affixed to the inner hull of the ship orspaced between the inner hull of the ship and the outer wall of thetank.

The ship 10 is of the double hull variety, as seen in FIG. 3, the hull12 being defined by an outer hull 20 and an inner hull 22. And, as seenin FIG. 1, the bottom of the ship is defined by an outer bottom 24 andan inner bottom 26. Between the inner bottom 26 of the ship 10 and thebottom of the tank 14, a plurality of keying and foundation members 28are illustrated. Anti-floatation chocks 30, located between transversebulkheads 32 and the tanks 14, harness the upward movement of the tanks14 in the event that the cargo hold should flood.

Now, with particular reference to FIGS. 2 through 4, the construction ofan embodiment of the inventive tank will be described. The cargo tank14, as noted above, is of the double wall variety. The primary barrier,or internal wall, is represented at 34 and the secondary barrier, orexternal wall, is represented at 36. The tank has a bottom 38, a top 40,a pair of internal sides 42 and 44, respectively, adjacent thetransverse bulkheads 32, and a pair of external sides, only one beingshown at 46, adjacent the inner hull 22. As is evident from the figures,both the internal wall 34 and the external wall 36 of the tank 14 arecorrugated, and are corrugated in the horizontal direction.

A corrugated longitudinal liquid-tight bulkhead 48 extends the entiredistance between and supports the inner sides 42 and 44 of the tank 14,and a corrugated transverse swash bulkhead 50 extends between andsupports the outer sides of the tank 14. In this manner, thelongitudinal liquid-tight bulkhead 48 and the transverse swash bulkhead50 divide the tank 14 into four substantially equal volumes.

A number of vertical webs 52, positioned both in the longitudinal andtransverse directions, extend into the body of the tank 14 and serve tosupport the primary barrier or internal wall 34 thereof. A number ofvertically oriented diaphragms 54 are welded both to the inner wall 34and the outer wall 36, are positioned in alignment with the verticalwebs 52 and support the secondary barrier 36.

In the described embodiment of the inventive tank, with the corrugationsoriented in the horizontal direction and with the vertical webspositioned in alignment with the vertical diaphragms, the horizontalstringers required in the cargo tank disclosed in the abovenotedcopending US. patent application become unnecessary. In the copendingpatent application, with the side wall corrugations oriented in avertical direction, and with the vertical webs and diaphragms positionedas there shown, the vertical webs and diaphragms did little to stabilizethe tank in the horizontal direction. With the side walls of the tankcorrugated in a horizontal direction, and with the webs and diaphragmsaligned, on the other hand, as in the presently described tank,horizontal stabilization is inherent. Therefore, the customaryhorizontal stringers may be eliminated, the construction of thedescribed horizontally corrugated cargo tank is less complex than thatassociated with the vertically corrugated cargo tanks known to the priorart and, as a consequence, the weight of the inventive tank is less thanthe weight of the known tanks.

As noted in the preceding paragraph, the horizontal corrugations and thealignment of the webs and diaphragms in the cargo tank described andillustrated herein eliminate the need for heavy horizontal stringers.However, even with the inventive tank, the innermost flanges of thevertical webs must be stabilized. As shown in the figures, these flangesare stabilized by a plurality of horizontal channel-shaped struts 56.Since the horizontal stringers disclosed in the abovereferencedcopending US. application serve the function of stabilizing the tankwalls in a horizontal direction, and since the struts 56 serve only thefunction of stabilizing the vertical webs, it should be evident that thestrength of the struts 56 need not be as great as the strength of thehorizontal stringers required in the prior art tanks. Therefore, thehorizontally corrugated cargo tank forming a part of the presentinvention is lighter in weight than the cargo tanks known to the priorart.

In FIGS. 3, 5, 6 and 7, the areas of intersection between the verticalwebs and the longitudinal and transverse bulkheads are shown. First, itshould be noted that the innermost regions of the vertical webs areprovided with flanges 58, these flanges serving as stays for preventingexcessive deflexion in their associated webs 52. It is the flanges, orstays which support the U-shaped channels 56.

The vertical webs 52, in the areas of intersection with the corrugatedbulkheads 48 and 50, are broken and are welded to the respectivebulkheads. Horizontal triangular plating members 60 are welded to thebulkheads 48 and 50, to the vertical webs 52 and to the flanges 58extending from the vertical webs. As seen in FIGS. 2 and 3, thetriangular plating members 60 are spaced, in a vertical direction, alongthe bulkheads 48 and 50.

The elements of the inventive tank are further stabilized by a series ofhorizontally oriented plating members located at critical areas in thetank. As seen in FIG. 3, these support members take the form of midtankplating elements 62 stabilizing the bulkheads 48 and 50 at their line ofintersection, corner plating elements 64 stabilizing the tank at itscorners, and side plating elements 66 serving to stabilize the bulkheads48 and 50 at the lines of intersection with the sides of the tank.

As seen in FIGS. 5 through 7, the transverse swash bulkhead 50 isprovided with a set of bulkhead openings 70, these openings reducing theundesirable splashing of the cargo during the voyage of the ship. Thelongitudinal bulkhead 48 may, if desired, be provided with a set ofopenings aligned and positioned so as to provide roll stabilization forthe ship when the tanks are charged with cargo.

As seen in FIGS. 4 and 8, the diaphragms 54 are also provided withopenings, these being shown at 72, positioned at the widest regionsbetween the corrugations defining the inner and outer walls of the tank.The openings 72 are important in that they provide means for physicalcommunication between areas defined by the diaphragms 54. If theopenings were not provided, there would be no available access forpurposes of inspecting the primary and secondary barriers of the tank.

Additional strength is provided by a plurality of longitudinal girders74 extending along the tank 14 and welded to the bottom wall thereof.The function of the girders 74 is to transmit foundation loads into thetank structure.

Now, with reference to FIGS. 1 through 4, the support and alignment ofthe tank 14 will be explained. As noted previously, the tank 14 isprovided with antifloatation chocks 30 serving to prevent the tank fromrising in its hold in the event that the hold should flood. As seen inthe figures, each anti-floatation chock 30 is defined by a flange 76attached to and extending from the respective side wall of the tank 14,and a flange 78, aligned with the flange 76, welded to the respectiveliquid-tight bulkhead 32 defining the cargo holds. As seen best in FIG.2, a small space is provided between the flanges 76 and 78, this spacepreventing contact between the elements of the anti-floatation chocks 30under all conditions save for hold flooding. The chocks 30 in no way addto the support of the tank 14.

As is evident from the figures, the tank is supported only at itsbottom, the tank-supporting structures serving also as keying elements.With more particular reference to FIGS. 2 and 4, the combination keyingand supporting elements will be described. A number of pedestals 80 arefixedly attached to the inner bottom 26 of the ship. And, adapted toassociate with the pedestals 80, a number of wooden insulating blocks82, as of balsa or fir, are attached to the outer wall 36 of the tank14, at the bottom thereof. The combination of the pedestals 80 and theinsulating blocks 82 make up tank foundations which transmit the loadsexerted by the tank to the structure of the ship. Due to the extremetemperature changes experienced by the tank, with its resultingcontractions and expansions, the pedestals 80 and the insulating blocks82 are associated in such a manner so as to allow sliding contacttherebetween.

It is important that the cargo tanks remain in relatively fixedpositions within their respective holds. Naturally, because of thecontractions and expansions experienced by the cargo tanks, they must befixed in a special manner. In the inventive tank, three lines offoundations are provided. Two lines are provided at the tank bottom nearthe hull of the ship, and the third line of foundation is provided alongthe center line of the ship, each line of foundation being oriented in alongitudinal direction. These foundations ensure that the tanks are heldrelatively fixed within their respective holds, allowing, of course, forexpansion and contraction.

As seen most clearly in FIG. 4, a keying arrangement is provided at thecentral region of the tank. This keying arrangement takes the form of anumber of transverse keys 84 rigidly secured to the inner bottom 26 ofthe ship and a number of transverse keys 86 rigidly secured to the outerwall 36 of the tank 14. As seen in this figure, the directions of thetransverse keys are made to alternate. In this. manner, the insulationblock 82 serves the dual function of insulating the tank 14 from thehull of the ship and also insulating the tank keys 86 from the ship keys84. For a full disclosure of this keying arrangement the attention ofthe reader is directed to US. Pat. No. 3,428,205, issued Feb. 18, 1969,and assigned to the present assignee.

As will be readily apparent when viewing FIGS. 2, 3 and 4, there arethree types of transitions between the sides, top and bottom of thecargo tank 14; and each of these transitions is done smoothly withoutthe necessity for complex and heavy box girder structures. The firsttype of corner transition is illustrated in FIG. 2 and is indicatedgenerally at 88; the second corner transition is illustrated in FIG. 3and is indicated generally at 90; and the third is illustrated in FIG. 4and is indicated generally at 92.

With reference first, to FIG. 2, the corner transition 88 will beexplained. This transition 88 may conveniently be termed a T transition.Here, the horizontal corrugations in the side walls are perpendicular tothe horizontal corrugations in the top and bottom walls. In this case,the transition between the side walls and the top and bottom walls ismade by abruptly ending the side wall corrugations at the widest regionthereof and by terminating the top and bottom corrugations by smoothlytapering these corrugations into flat plates spaced apart by the maximumdistance between the corrugations. From FIG. 2, it can be seen that thesmooth corner transitions require no T-welds or box girder structures.Further, because of the smoothness of the transition, local areas ofextreme stress are avoided.

In FIG. 3, the second type of corner transition, transition 90, will beexplained. Transition 90 may be termed an L transition. Here, while theside all corrugations are perpendicular to the top and bottom wallcorrugations, an L is defined at the intersection. This transition isdeveloped, both at the top and bottom walls, by smoothly tapering bothsets of corrugations into flat plates spaced apart by a distance equalto a maximum corrugation spacing. Again, the transition is madesmoothly, thus avoiding the necessity for box girders and T-welds andeliminating localized stress concentration.

In FIG. 4, the last type of corner transition, indicated at 92, isillustrated. This type of corner transition 92 may be termed a paralleltransition, for the side wall corrugations are parallel to the top andbottom wall corrugations. Here, the mating is carried out by abruptlyending the corrugations in the side walls, the top and the bottom, atthe region where the distance between the outer and inner walls of thetank are maximum, the corners being defined by smoothly curved plates.Again the comer is defined without the use of box girders, withoutT-welds and without areas of local stress concentration.

In FIG. 10, a typical corner transition is illustrated in perspective.Here, it can be seen that the transition is smooth and that it isdesigned so that the maximum distance between the corrugated tank wallsis utilized. The construction of the corner is as follows.

Corrugation transition pieces 100 are fit on each of the corrugatedwalls and are designed to gradually taper the corrugations to a flatplate. The transition pieces 100 are welded to their respectivecorrugated walls by a butt weld, seen at 102. The two transition piecesare then butt welded to a vertical arcuate corner piece 104, and thevertical transition is completed. The remaining portions of the cornertransition illustrated in FIG. 10 are completed by similarly joining thetank top to its adjacent tank side walls by means of horizontal arcuatecorner pieces 106 and by fitting the one eighth spherical comer piece108 between the respective corner pieces 104 and 106.

From the above description of the three types of comer transitions, theadvantages of the inventive corrugated tank should be clear. With thesmooth transitions described above, the standard box girder structuresare eliminated. This results both in weight savings and cost savings.And, because the transitions are smooth, rather than abrupt, all T-weldsare avoided, these being replaced by butt welds or seam welds. As notedpreviously, butt and seam welds are less difficult to perfect than areT-welds, and are more readily checked for faulty welds by radiographicanalysis. Further, due to the'smooth transitions at the tank corners,excessive areas of stress concentration are avoided.

Now, with reference to FIGS. 8a and 8b, the corrugated top and sides ofthe tank, and the corrugated bottom of the tank will be described. Theside and top corrugations are shown at 94 and the bottom corrugationsare shown at 96. As can be seen, the depth of the corrugations in thetop and sides of the tank is less than the depth of the corrugations inthe bottom of the tank. This is the result of the relationship betweenthe depth of the corrugation and the amount of stiffening provided bythe corrugated wall. That is, the greater is the depth of thecorrugation, the greater is the stiffening. Naturally, because thestress experienced by the bottom of the tank is substantially greaterthan the stress experienced by the sides and top of the tank, it isdesirable that the bottom of the tank be structurally more sound thanthe remaining portions of the tank.

As can be seen in FIGS. 8a and 8b, the depth of the corrugations in thesides and top is 10 inches and the depth of the corrugations in thebottom is l 1% inches. Naturally, these dimensions are given as examplesonly, and may be varied in accordance with the structural requirementsof the particular tank. Further, while the sides and top could becorrugated to 11 inches, for uniformity, such design would beeconomically unsound.

The smallest distance between the tank corrugations, both in FIG. 8a andFIG. 8b, is approximately 10 inches. As noted previously, this dimensionmight be increased so as to provide for inspection access between allportions of the corrugated walls. For example, the narrowest dimensionmight be increased from approximately 10 inches to approximately 18inches, the 18 inch dimension allowing passage of the man of averagesize.

As also seen in FIGS. 8a and 8b, the flats on the corrugations arelonger in the corrugated bottom 96 than in the corrugated top and sides94 of the tank. The increased depth of the corrugations in the bottomwall and the placement of the longitudinal girders make such increaseddimension possible. Naturally, the specific dimensions of thecorrugations depend upon the use of the tank and the anticipated stressexpected to be encountered thereby.

Above, several embodiments of the present invention have been described.It should be appreciated, however, that these embodiments are describedfor purposes of illustration only and that numerous alterations andmodifications may be practiced by those skilled in the art withoutdeparting from the spirit and scope of the invention. Accordingly, it isthe intent that the invention not be limited by the above but be limitedonly as defined in the appended claims.

We claim:

1. A double wall cargo tank for the marine transportation of liquefiedgases, such as methane and the like, at atmospheric pressure and atcryogenic temperature, the cargo tank comprising: an inner wall havingcorrugations defined therein, said inner walldefining a firstliquid-tight enclosure; an outer wall having corrugations definedtherein, spaced from and enclosing said inner wall, said outer walldefining a second liquid-tight enclosure; a wall space defined betweensaid inner and said outer walls, said inner and said outer walls beingarranged so that their undulations projecting into the wall space arealigned and in opposed relation perpendicularly of the planess of thewalls and their undulations projecting out of the wall space are alignedand in opposed relation perpendicularly of the planess of the walls; aplurality of webs rigidly connected to said corrugated inner wall,extending into the tank defined by said inner wall a substantial portionof the transverse dimensions of the tank defined by said inner wall,said webs extending transversely of said inner wall corrugations andserving to support said inner wall; a plurality of diaphragms, eachrigidly connected both to said inner and said outer walls, each havingits plane positioned within said wall space, and each being aligned withthe plane of a respective web, said diaphragms serving to support saidouter wall; and means for stabilizing the portions of said websextending into the tank defined by the inner wall including a pluralityof struts, eachof said struts extending perpendicularly and beingrigidly connected to the innermost region of selected ones of said webs.

2. The cargo tank defined in claim 1, and further comprising a pluralityof spaced longitudinal girders rigidly connected to the bottom of saidcargo tank and serving to transmit foundation loads into the tankstructures.

3. The cargo tank defined in claim 1, and further comprising entry meansfor gaining access to said wall space.

4. The cargo tank recited in claim 1, wherein the corrugations on thetank bottom are of a depth different than the corrugations in the tanktop and sides.

5. The cargo tank defined in claim 1, wherein said cargo tank is mountedin the hold of a ship, and further comprising: support members forsupporting the cargo tank only at the bottom thereof.

6. The cargo tank recited in claim 5, wherein said support members servethe dual function of supporting and keying said tank.

7. The cargo tank recited in claim 5, and further comprisinganti-floating chocks for preventing the tank from rising in its hold ifsaid hold should become flooded.

8. The cargo tank recited in claim 1, wherein the corrugations in thetank side walls are horizontally oriented.

9. The cargo tank recited in claim fi, wherein said webs and saiddiaphragms are vertically oriented.

10. The cargo tank recited in claim 1, and further comprising: alongitudinal bulkhead dividing the cargo tank into two sections of equalvolume; and a transverse swash bulkhead dividing the cargo tank into twosections of approximately equal volume; said longitudinal and transversebulkheads, together, dividing the cargo tank into four compartments ofequal volume.

11. The cargo tank recited in claim 10, wherein said bulkheads arecorrugated.

12. The cargo tank recited in claim 10, wherein both the longitudinaland the transverse bulkheads are provided with a plurality of openingstherein, these openings providing communication between each of saidfour compartments of equal volume.

13. The cargo tank recited in claim 12, wherein the minimum spacingbetween the inner and the outer walls of said cargo tank permits thepassage of a workman for purposes of inspection.

14. The cargo tank recited in claim 1, wherein the transitions betweenthe top, sides and bottom of said tank are smooth transitions.

15. The cargo tank defined in claim 14, wherein the corrugations in thetop of the tank are oriented in the same direction as are thecorrugations in the bottom of the tank.

16. The cargo tank defined in claim 14, wherein all welds in both theinner and the outer walls are either seam welds or butt welds.

17. The cargo tank recited in claim 14, wherein certain of thetransitions between the tank sides and the tank top and bottom comprise:a pair of smoothly curved plates associated, respectively, with saidinner and said outer walls and adapted to rigidly connect the tank sidesto the associated tank top or tank bottom; a pair of taper regionsassociated, respectively, with said inner and said outer walls in thetank top or the tank bottom wherein the corrugated inner and outer wallsare tapered into flat plates, the spacing between the flat plates insaid taper regions being equal to the maximum spacing between thecorrugated inner and outer walls; said smoothly curved plates each beingconnected, at one side, to a respective flat plate in a taper region,and, at the other side, to the associated tank sides at an area ofmaximum spacing between the corrugated inner and outer walls.

18. The cargo tank recited in claim 14, wherein certain of thetransitions between the tank sides and the tank top and bottom comprise:a pair of smoothly curved plates associated, respectively, with saidinner and said outer walls and adapted to rigidly connect the tank sidesto the associated tank top or tank bottom; a first pair of taper regionsassociated, respectively, with said inner and said outer walls in thetank top or the tank bottom wherein the corrugated inner and outer wallsare tapered into flat plates, the spacing between the flat plates insaid taper regions being equal to the maximum spacing between thecorrugated inner and outer walls; a second pair of taper regionsassociated, respectively, with said inner and said outer walls in thetank sides wherein the corrugated inner and outer walls are tapered intoflat plates, the spacing between the flat plates in said taper regionsbeing equal to the maximum spacing between the corrugated inner andouter walls;

said smoothly curved plates each being connected, at one side, to arespective flat plate in said first pair of taper regions, and, at theother side, to a respective flat plate in said second pair of taperregions.

19. The cargo tank recited in claim 14, wherein certain of thetransitions between the tank sides and the tank top and bottom comprise:a pair of smoothly curved plates associated, respectively, with saidinner and said outer walls and adapted to rigidly connect the tank sidesto the associated tank top or tank bottom; said smoothly curved plateseach being connected, at one side, to a wall of the associated tank sideat an area of maximum spacing between the corrugated inner and outerwalls, and, at the other side, to a wall of the associated tank top orbottom at an area of maximum spacing between the corrugated inner andouter walls.

20. The cargo tank defined in claim 14 wherein certain of thetransitions between the tank sides and between the tank sides and thetank top and bottom comprise:

corrugation transition pieces each rigidly connected,

respectively, to an inner and an outer side wall of the tank;cylindrical cylindrical vertical corner pieces of arcuate transversecross section rigidly connected between respective pairs of saidtransition pieces that are rigidly connected to adjacent sides of thetank;

cylindrical horizontal corner pieces of arcuate transverse crosssection, each connected, respectively, between an inner and an outerwall of the tank sides and an inner and an outer wall of the tank topand bottom; and

additional comer pieces connected between respective ones of saidvertical comer pieces and said horizontal comer pieces.

21. The cargo tank as in claim 20 wherein said additional corner pieceseach define a smooth surface defining one-eighth ofa sphere.

22. The cargo tank as in claim 20 wherein said corrugation transitionpieces each define along its length a series of transversechannel-shaped members of varying depth defined by a firsttrapezoidal-shaped surface, first and second triangular-shaped surfacesconnected to said first trapizoidal-shaped surface, and first and secondrectangular-shaped surfaces connected, respectively, to said first andsecond triangular-shaped surfaces.

23. The cargo tank as in claim 22 wherein said triangular-shapedsurfaces and said rectangular-shaped surfaces are coplanar withpredetermined portions of said tank sides.

1. A double wall cargo tank for the marine transportation of liquefiedgases, such as methane and the like, at atmospheric pressure and atcryogenic temperature, the cargo tank comprising: an inner wall havingcorrugations defined therein, said inner wall defining a firstliquid-tight enclosure; an outer wall having corrugations definedtherein, spaced from and enclosing said inner wall, said outer walldefining a second liquid-tight enclosure; a wall space defined betweensaid inner and said outer walls, said inner and said outer walls beingarranged so that their undulations projecting into the wall space arealigned and in opposed relation perpendicularly of the planess of thewalls and their undulations projecting out of the wall space are alignedand in opposed relation perpendicularly of the planess of the walls; aplurality of webs rigidly connected to said corrugated inner wall,extending into the tank defined by said inner wall a substantial portionof the transverse dimensions of the tank defined by said inner wall,said webs extending transversely of said inner wall corrugations andserving to support said inner wall; a plurality of diaphragms, eachrigidly connected both to said inner and said outer walls, each havingits plane positioned within said wall space, and each being aligned withthe plane of a respective web, said diaphragms serving to support saidouter wall; and means for stabilizing the portions of said websextending into the tank defined by the inner wall including a pluralityof struts, each of said struts extending perpendicularly and beingrigidly connected to the innermost region of selected ones of said webs.2. The cargo tank defined in claim 1, and further comprising a pluralityof spaced longitudinal girders rigidly connected to the bottom of saidcargo tank and serving to transmit foundation loads into the tankstructures.
 3. The cargo tank defined in claim 1, and further comprisingentry means for gaining access to said wall space.
 4. The cargo tankrecited in claim 1, wherein the corrugations on the tank bottom are of adepth different than the corrugations in the tank top and sides.
 5. Thecargo tank defined in claim 1, wherein said cargo tank is mounted in thehold of a ship, and further comprising: support members for supportingthe cargo tank only at the bottom thereof.
 6. The cargo tank recited inclaim 5, wherein said support members serve the dual function ofsupporting and keying said tank.
 7. The cargo tank recited in claim 5,and further comprising anti-floating chocks for preventing the tank fromrising in its hold if said hold should become flooded.
 8. The cargo tankrecited in claim 1, wherein the corrugations in the tank side walls arehorizontally oriented.
 9. The cargo tank recited in claim 8, whereinsaid webs and said diaphragms are vertically oriented.
 10. The cargotank recited in claim 1, and further comprising: a longitudinal bulkheaddividing the cargo tank into two sections of equal volume; and atRansverse swash bulkhead dividing the cargo tank into two sections ofapproximately equal volume; said longitudinal and transverse bulkheads,together, dividing the cargo tank into four compartments of equalvolume.
 11. The cargo tank recited in claim 10, wherein said bulkheadsare corrugated.
 12. The cargo tank recited in claim 10, wherein both thelongitudinal and the transverse bulkheads are provided with a pluralityof openings therein, these openings providing communication between eachof said four compartments of equal volume.
 13. The cargo tank recited inclaim 12, wherein the minimum spacing between the inner and the outerwalls of said cargo tank permits the passage of a workman for purposesof inspection.
 14. The cargo tank recited in claim 1, wherein thetransitions between the top, sides and bottom of said tank are smoothtransitions.
 15. The cargo tank defined in claim 14, wherein thecorrugations in the top of the tank are oriented in the same directionas are the corrugations in the bottom of the tank.
 16. The cargo tankdefined in claim 14, wherein all welds in both the inner and the outerwalls are either seam welds or butt welds.
 17. The cargo tank recited inclaim 14, wherein certain of the transitions between the tank sides andthe tank top and bottom comprise: a pair of smoothly curved platesassociated, respectively, with said inner and said outer walls andadapted to rigidly connect the tank sides to the associated tank top ortank bottom; a pair of taper regions associated, respectively, with saidinner and said outer walls in the tank top or the tank bottom whereinthe corrugated inner and outer walls are tapered into flat plates, thespacing between the flat plates in said taper regions being equal to themaximum spacing between the corrugated inner and outer walls; saidsmoothly curved plates each being connected, at one side, to arespective flat plate in a taper region, and, at the other side, to theassociated tank sides at an area of maximum spacing between thecorrugated inner and outer walls.
 18. The cargo tank recited in claim14, wherein certain of the transitions between the tank sides and thetank top and bottom comprise: a pair of smoothly curved platesassociated, respectively, with said inner and said outer walls andadapted to rigidly connect the tank sides to the associated tank top ortank bottom; a first pair of taper regions associated, respectively,with said inner and said outer walls in the tank top or the tank bottomwherein the corrugated inner and outer walls are tapered into flatplates, the spacing between the flat plates in said taper regions beingequal to the maximum spacing between the corrugated inner and outerwalls; a second pair of taper regions associated, respectively, withsaid inner and said outer walls in the tank sides wherein the corrugatedinner and outer walls are tapered into flat plates, the spacing betweenthe flat plates in said taper regions being equal to the maximum spacingbetween the corrugated inner and outer walls; said smoothly curvedplates each being connected, at one side, to a respective flat plate insaid first pair of taper regions, and, at the other side, to arespective flat plate in said second pair of taper regions.
 19. Thecargo tank recited in claim 14, wherein certain of the transitionsbetween the tank sides and the tank top and bottom comprise: a pair ofsmoothly curved plates associated, respectively, with said inner andsaid outer walls and adapted to rigidly connect the tank sides to theassociated tank top or tank bottom; said smoothly curved plates eachbeing connected, at one side, to a wall of the associated tank side atan area of maximum spacing between the corrugated inner and outer walls,and, at the other side, to a wall of the associated tank top or bottomat an area of maximum spacing between the corrugated inner and outerwalls.
 20. The cargo tank defined in claim 14 wherein certain of thetransitions between the tank sides and between the tank sides and thetank top and bottom comprise: corrugation transition pieces each rigidlyconnected, respectively, to an inner and an outer side wall of the tank;cylindrical cylindrical vertical corner pieces of arcuate transversecross section rigidly connected between respective pairs of saidtransition pieces that are rigidly connected to adjacent sides of thetank; cylindrical horizontal corner pieces of arcuate transverse crosssection, each connected, respectively, between an inner and an outerwall of the tank sides and an inner and an outer wall of the tank topand bottom; and additional corner pieces connected between respectiveones of said vertical corner pieces and said horizontal corner pieces.21. The cargo tank as in claim 20 wherein said additional corner pieceseach define a smooth surface defining one-eighth of a sphere.
 22. Thecargo tank as in claim 20 wherein said corrugation transition pieceseach define along its length a series of transverse channel-shapedmembers of varying depth defined by a first trapezoidal-shaped surface,first and second triangular-shaped surfaces connected to said firsttrapizoidal-shaped surface, and first and second rectangular-shapedsurfaces connected, respectively, to said first and secondtriangular-shaped surfaces.
 23. The cargo tank as in claim 22 whereinsaid triangular-shaped surfaces and said rectangular-shaped surfaces arecoplanar with predetermined portions of said tank sides.